This article was originally published by Hakai Magazine.
Witnessing a great white shark emerge from the ocean, its powerful jaws gripping a shocked seal, provides a glimpse into the pinnacle of predatory ability. However, this perception was challenged in South Africa when killer whales demonstrated that even great white sharks have reasons to fear.
Long before their infamous encounters with yachts, killer whales made headlines for a series of attacks on South African great white sharks. The attacks were both gruesome and impressive, as the killer whales displayed a discerning taste by consuming the sharks’ nutrient-rich livers and discarding the rest to sink or wash ashore on nearby beaches.
As news spread about these attacks, another strange phenomenon unfolded. Great white sharks began disappearing from their well-known habitats in South Africa’s False Bay and Gansbaai regions, causing widespread speculation and concern.
Ecologist Michelle Jewell from the Michigan State University Museum explains, “The decline of white sharks was so dramatic, so fast, so unheard-of that lots of theories began to circulate.” One theory suggested that overfishing of the sharks’ prey to meet Australia’s fish-and-chips market demands led to their decline, although some scientists disputed this idea. Others speculated that the killer whales were responsible for the shark disappearances, suggesting that they were killing all of the sharks.
Heather Bowlby, a shark expert with Fisheries and Oceans Canada, emphasizes the conservation concerns associated with significant population declines in local areas. The sudden absence of great white sharks in previously frequented locations sparked worries that they had all perished.
However, scientists now have a better understanding of what transpired. According to a recent paper by Bowlby and her colleagues, the killer whales caused the sharks’ disappearance, but the sharks weren’t eradicated. Instead, they migrated. Extensive research revealed a significant eastward shift in the white shark population across South Africa.
Jewell, who was not involved in the study, finds this migration unsurprising, stating, “We know that predators heavily influence the movement and habitat selection of their prey, so this shouldn’t come as a shock. The issue is that many people didn’t consider great white sharks as prey.”
Alison Kock, a marine biologist with South African National Parks and co-author of the study, explains that reports of white shark sightings in eastern sites led to the resolution of this mystery. She says, “As False Bay and Gansbaai experienced significant declines, other areas reported a surge in white shark populations, which was too rapid to be attributed to reproduction alone.”
Kock adds, “It had to be redistribution. The white sharks moved east.” While places like Algoa Bay had previously seen great white sharks, the recent numbers were unprecedented.
In the absence of white sharks, South Africa’s west coast is undergoing changes. New species such as bronze whalers and seven-gill sharks have appeared in False Bay. Shark diving tour operators in the area have faced challenges, with some transitioning to kelp-forest dives due to the popularity of the documentary My Octopus Teacher. Unfortunately, many operators have ceased operations.
The consequences of the great white sharks’ relocation to the east remain unknown. Scientists anticipate significant ecological changes and potential increases in shark-human interactions, as residents in these newfound shark habitats are not accustomed to such encounters.
Although the exact number of white sharks killed in killer whale attacks may never be known, the killer whales’ choice to primarily consume the sharks’ livers, which help them float, suggests that many dead white sharks may have sunk without a trace. Nonetheless, Kock is relieved that the mystery has been solved.
She says, “This has been very worrying for me, and it was good to see evidence that they hadn’t all died. But it’s still unbelievable to me that I can go to [False Bay’s] Seal Island and not see any white sharks. It’s something I never expected, and I miss them a lot.”
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